Electrochemical cells, batteries, have existed in a wide variety of physical configurations for an even wider variety of uses. The physical characteristics of battery housings have been dictated by a plethora of oftentimes conflicting considerations, including size, weight, interchangeability, and physical conformance to the devices into which they fit. In the case where batteries are sought to be employed to power electrical vehicles, the higher voltages needed for powering automotive electric engines dictate a larger number of individual cells. The problems associated with the utilization of a large number of cells in series in the automotive environment are many. For example, in U.S. Pat. No. 4,734,342 which issued on Mar. 29, 1988 to Harvey N. Seiger, entitled "Terminal Means For Electrochemical Cells," it is reported that the current distribution pattern in a group of series connected batteries approaches an elliptical profile. The result is an uneven or non-uniform current distribution through the cell and, consequently, non-uniform active metal consumption over the areas of the bipolar electrodes.
Another problem is the "dead," or open-circuited cell. As cells are discharged and recharged, the growth of the electrodes may be such that an electrical open circuit is formed across the plates of a bipolar cell. When this occurs in a single cell of a 6 cell, 12 volt battery, the entire battery must be discarded. The concomitant discarding of the other five functioning cells. In the case of an electric vehicle, the dead cells causing the dead battery necessitates an immediate replacement. However, most electric car operators are not immediately equipped to change the dead battery in the event of a failed cell. Even in cases where the non-working battery could be replaced, the liability relating to the weight of transporting a spare 12 volt battery would significantly reduce the efficiency and range of the electric vehicle.
Admittedly, a series of 12 volt batteries employed in an electrical vehicle could be charged one at a time, but this would not only be onerous and burdensome, but the charging of any one cell or group of cells, without regard to the state of other cells, will not enable the true control of charging.
The use of stacked cells is also well-known in the battery art, but generally offers very limited flexibility and the ability to handle the needs of individual cells, and to control the individual cells on an individual basis. For example, U.S. Pat. No. 5,002,841 to Belongia et al., which issued on Mar. 6, 1991 and entitled "Composite End Block For A Battery" disclosed a series of exterior alternating separators to form a stack of electrochemical cells. A lightweight deflection-resistant end block was provided in an attempt to form an overall sealed mass.
U.S. Pat. No. 4,687,717 issued to Kaun et al. on Aug. 18, 1987 and entitled "Bi-Polar Battery With Array of Sealed Cells" discloses a gas-tight housing compressibly enclosing a series of horizontally disposed cells. U.S. Pat. No. 3,844,841 to Bernard Baker which issued on Oct. 29, 1974 and entitled "Modular Battery Construction" discloses packs of wafer-like battery cells fitted within an overall housing which may be fitted adjacent similarly-shaped and housed sets of wafer cells. The wafer cells are wired together, and have internal wiring extending between circular metallic electrode connectors. U.S. Pat. No. 438,827 to E. N. Reynier, issued on Oct. 21, 1890 and entitled "Secondary Battery" also discloses a rigid box for holding a series of vertically disposed battery cells. U.S. Pat. No. 4,189,528 to Ronald I. Clutwick on Feb. 19, 1980 and entitled "Power Module Assembly" again disclosed a very closely stacked array of cells, but utilizing a sealed bag pressure device to ensure close compression of the cells.
In all the foregoing battery configurations, there is no provision made for rapid interchange of dead, open-circuited cells. Reynier illustrates some parallel connection of the individual cells, no provision is made for selective disengagement of any one cell, either electrically or physically, from the main battery array.
Further, the above patented designs are not advantageous in electrical vehicle use, and particular as a use for retrofit with regard to an electrical vehicle conversion from a fossil fuel burning vehicle. Current configurations for electric vehicles require the purchase a plurality of 6 or 12 volt batteries to provide the 72 to 120 or more volts of electricity necessary to power the vehicle. These batteries are then connected in series with heavy electrical cables. The batteries are then charged and discharged in series through the system of heavy cables, requiring a long charging time. In this configuration, the batteries must be carefully matched in order to derive the most efficiency from the system. The weakest battery, actually the weakest cell, in the series determines the degree to which the system can be charged or discharged. If a single battery and its multiple cells is replaced, the new battery can contribute no more to the system than the weakest battery remaining in the system. The batteries when configured in series as outlined, must be maintained at a nearly full charge condition to extend their operating life. If the batteries are allowed to stand for any length of time in a discharge state, they will rapidly deteriorate.
These factors are especially applicable to the deepcycle lead acid battery. The lead acid battery is the battery of choice in the electrical vehicle applications because of its self-containment, mass production abilities, reliability and inexpensiveness.
Both the references pointed out above, and the standard lead-acid batteries are typically not specifically optimized for electric vehicle usage. Rapid replacement of individual cells in both configurations is prohibitive. There is no means for charging individual cells when the system is under load. The weakest cells in the system configuration are not amenable to a trickle charge to take account of cell weakness. Lastly, rapid charge of the cells can not be had without significant un-wiring of the cables or other changes in wiring.
What is therefore needed is an electric vehicle battery system which enables as many advantages from other battery systems to be employed in order to make the system practical and highly useable. The desired system should have individual cells which may be accessed, changed, monitored, individually charged, and, if necessary, individually discharged.